Cracking the Code for Hummingbird Syndrome – UofSC News & Events

Biological science professor Carolyn Wessinger wants to know why wildflower species evolved to change pollinators – and what it means

Posted: November 3, 2021; Updated on: November 3, 2021
By Patrick Wall

To understand the research of Carolyn Wessinger, assistant professor of biological sciences at the University of South Carolina, you need to know about birds and bees.

Once upon a time there were many species of the genus wildflowers Penstemon bloomed with short, broad spikes of brilliant bluish-purple flowers. The flowers attracted bees, which stuffed their stocky bodies between the petals to reach the nectar inside and spread the pollen as they took to the skies.

But somewhere in evolutionary time – thousands to millions of years, says Wessinger – 40 Penstemon the species have changed. The bluish flowers turned a brilliant purple and produced more nectar. Compact petals stretched into deep, drooping tubes. Plants evolved, but their adaptations made them less attractive to bees, who had no room to land on flowers and couldn’t even see the flowers initially.

I like the work in the field. I love being outside looking at these plants.

Carolyn Wessinger, Assistant Professor of Biological Sciences

But the new traits attracted a new pollinator: hummingbirds, which needed the extra nectar to fuel their overactive metabolism. Their sharp beaks could reach the nectar at the base of the petals. And, because hummingbirds soar as they feed, they didn’t need a place to land.

The lines evolved so frequently and so steadily that researchers found a name for it.

“We call it hummingbird syndrome,” she says.

Understanding hummingbird syndrome goes beyond simply satisfying scientific curiosity. The fundamental question of his research – What is the source of genetic variation for adaptation? – could uncover clues as to the possibility and speed with which species could develop new traits to adapt to environmental changes, such as those caused by climate change.

“Understanding the constraints on the process of evolutionary change – even in this group of wildflowers that is not of direct economic importance – can be very important for making broader generalizations, when put into the context of the results. other study systems, ”she said. .

Wessinger studied the Penstemon flight from bee pollination to hummingbird pollination for years to deepen understanding of convergent evolution – essentially, how different species independently develop similar characteristics to accommodate similar needs. In June, Wessinger and his research group received a five-year grant from the National Science Foundation to continue this research. Wessinger received NSF scholarships as a doctoral student and post-doctoral researcher, but the June scholarship is her first scholarship as a principal investigator.

So far, Wessinger’s research has yielded some fascinating results. The repeated changes from purple flowers to reds, Wessinger says, involve loss of function. The gene that controls the enzymatic steps to produce the pigment violet is somehow inactivated.

“So that means you can basically mess up the genes that produce purple flowers and end up with a red flower,” says Wessinger. Indeed, she adds, it is natural selection in action – and it can be a particularly useful short-term strategy if a
Penstemon the flower needs to change pollinator.

But Wessinger also found that the exchange of pollinators can delay species diversity. Once a branch of the Penstemon the family tree passes to pollination by hummingbirds, the evolution of new species on this branch slows down or stops. And Wessinger’s research suggests that Penstemon species that change pollinators cannot go back. She has a few ideas as to why: it might be impossible to reactivate genes once they’ve been turned off, she reasoned, or it could be a matter of ecology.

Either way, there is still a lot to learn. Wessinger has a good understanding of how flower color has changed, but is less sure about the genetics behind the changes in flower shape and nectar production. There are also questions about introgression – when species transfer genetic information through hybridization. If, in fact, hybridization has resulted in the movement of hummingbird-pollinated traits between lineages, Wessinger says, then scientists can make predictions about how natural selection acts on these plants in real time.

“A fundamental question we ask ourselves as evolutionary biologists is whether the repeated evolution of a given trait – this phenomenon of convergent evolution – really involves new mutations in each lineage, or if that trait perhaps has be evolved into a lineage but has been transferred to a new lineage by an interspecific hybridization process, which can be quite common in plants, ”says Wessinger. “And so it is the objective of this grant, to assess whether this process of hybridization between different lines has contributed to this model of convergent evolution.”

Understanding the constraints on the process of evolutionary change … can be very important in making broader generalizations.

Carolyn Wessinger, Assistant Professor of Biological Sciences

Penstemon is an ideal avenue for studying evolutionary change, says Wessinger, because wildflowers have abandoned bees for hummingbirds so many times, leaving a large pool of data to draw on. Wessinger’s current research focuses on natural hybrids Penstemon populations on the border between Utah and Arizona, about 20 miles south of Zion Canyon.

Over the next few years, Wessinger and his team will roam these lands, collect samples of hybrid wildflowers, and bring them back to the lab for genome sequencing to determine the amount of genetic material from each parent. They will also record phenotypic data and photograph flowers and analyze their spectral reflectance data to understand how different pollinators might see these flowers.

Analyzing all of this data is exciting, says Wessinger, and brings it one step closer to discovering the code for hummingbird syndrome. But for Wessinger, research is as exciting as discovery.

“I like the work in the field,” she says. “I love being outside looking at these plants.”

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Subjects: Faculty, Research, College of Arts and Sciences